UART and USART Debugging and Error Handling#

This guide explains how to debug and handle errors in Universal Asynchronous Receiver/Transmitter (UART) and Universal Synchronous/Asynchronous Receiver/Transmitter (USART) communication. It provides checklists, hardware and software debugging steps, error code handling, and additional troubleshooting methods.

Common Debugging Tips#

Start with general debugging practices before moving to advanced tools.

Refer to the official troubleshooting guide for application debugging: WiseConnect Debugging Guide.

Debugging UART/USART Connections#

Debugging connections involves checking hardware integrity, verifying configurations, and using specialized tools for signal analysis.

1. Visual Inspection and Connection Checklist#

• Ensure the transmit (TX) and receive (RX) lines are correctly connected between devices.

• Check that voltage levels are correct (for example, 3.3 V or 1.8 V).

• Verify ground connections between all boards.

• Confirm the correct pin mapping and alternate function selection for UART/USART pins.

2. Interfacing with Si91x Development Kits (Full or Half Duplex Setup)#

When using Si91x development kits, configure one board as the UART/USART transmitter and the other as the receiver.

• For RS485, ensure that driver enable (DE) and receiver enable (~RE) signals are correctly configured and toggled.

• Use Simplicity Studio to flash and debug firmware on both boards. Run UART transactions and monitor activity with a logic analyzer and Studio debug tools.

• For multi-drop or addressable setups, verify address-match logic and use 9-bit addressing if required.

Example setup diagram:

3. Using a Logic Analyzer for Debugging#

A logic analyzer (LA) helps confirm signal integrity and protocol decoding.

• Connect LA probes to TX and RX lines.

• Configure the LA for UART protocol decoding by setting the correct voltage threshold and baud rate.

• Capture transactions during UART operations.

• Use the analyzer to verify:

  • Start and stop bits

  • Data bytes

  • Parity and framing

  • Timing and baud rate accuracy

Example LA capture:

The following capture shows UART communication between two Si91x development boards using the blocking transfer example.

4. Debugging with Simplicity Studio and a Logic Analyzer#

Integrating Simplicity Studio with a logic analyzer provides synchronized hardware and software debugging.

• Open Simplicity Studio and switch to the Debug perspective.

• Flash firmware and connect the LA to TX and RX lines.

• Use the LA plugin or external LA software to view UART signals.

• Set breakpoints to correlate code execution with captured signals.

Error Code Handling#

The UART/USART driver uses standardized status codes to indicate operation results. APIs such as sl_si91x_usart_send_data() and sl_si91x_usart_receive_data() return these codes.

Use these codes to identify causes such as misconfigured pins, incorrect baud rates, or communication errors.

If the UART/USART peripheral enters an undefined or error state (for example, framing error, missed data, or improper sleep transition), reset the peripheral:

sl_si91x_usart_deinit(uart_handle);
sl_si91x_usart_init(UART_1, &uart_handle);

Additional Debugging Tips#

Apply these additional methods for more effective debugging.

• Use DEBUGOUT or similar macros to print error codes and statuses in firmware.

• Check for shorted lines, incorrect voltage levels, or missing connections if communication fails.

• Use a logic analyzer to diagnose timing mismatches, framing errors, or data loss.

• For WiseConnect 3, use enhanced debug and protocol analysis features in Simplicity Studio.

Flow Control Debugging#

Ensure that flow control is configured correctly to prevent data loss.

• Enable both Request to Send (RTS) and Clear to Send (CTS) for automatic flow control.

• Use status registers to check First In, First Out (FIFO) levels and flow control status.

• Poll the "FIFO full" status before writing to the transmitter FIFO.

Debugging in RS485 Mode#

For RS485 communication, verify the following:

• DE and ~RE signals are correctly configured and toggled.

• Multi-slave setups use 9-bit addressing with verified address-match logic.